This invention relates to a read head for providing an electrical pulse in response to a switch in state of the magnetic wire known as Wiegand Wire. The Wiegand Wire is a ferro magnetic wire having core and shell portions with divergent magnetic properties. These wires have come to be known in the art as Wiegand Wires. The currently preferred type of Wiegand Wire is disclosed in U.S. Pat. No. 4,247,601 issued on Jan. 27, 1981 to John Wiegand. A read head which is effective to provide an output pulse from the switch in state of the Wiegand Wire is described in U.S. Pat. No. 4,263,523 issued Apr. 21, 1981.
The wire switches state when the magnitude of an external magnetic field passes a threshold value.
One of the objects in the design of a read head is to establish the external field such that the threshold field is properly positioned immediately adjacent to the pick-up coil. Then when the Wiegand Wire switches state, there will be a maximum coupling of the changing magnetic field to the pick-up coil.
Another object in the design of a read head for use with the Wiegand Wire is to provide as compact a read head as possible so that the number of applications in which it may be employed is maximized. For example, the use of a Wiegand Wire in access cards and keys involves a large variety of environments and dimensional circumstances. The narrower the read head, the more readily can a particular installation adapt to the use of a Wiegand Wire encoded access card or access key.
The smaller the read head structure, the greater will the Wiegand Wire itself influence or distort the external field generated by the read head. One of the main factors in limiting the density in which the Wiegand Wire bits can be deployed in an access card or access key is the influence of the Wiegand Wire itself on the magnetic field generated by the read head.
Accordingly, the major objects of this invention are to provide a more compact read head with a more controlled external field that is less influenced by the passage across the read head of the Wiegand Wire being read.
A related purpose is to provide a read head design which will permit a closer deployment of the individual bits represented by each Wiegand Wire.